An insect species that outlived the dinosaurs and survived the onslaught of unchecked water pollution is now so numerous as it emerges from the waters of Lake Erie that clouds of mating adults are visible on weather radar.
The annual mayfly “hatch” of perhaps one-quarter trillion individuals in Lake Erie’s Western Basin has largely occurred. It will resume next May and June. That is when another emergence will occur; the nymphs that hatched from fertilized eggs deposited this year or no more than two years ago ascending to the water’s surface to become winged adults.
Thus their life as nymphs is brief enough even while their sexually mature adult versions are measured in an eye blink. Depending upon a specific mayfly species, a male will live for no more than two days. An adult female mayfly will live as little as five minutes and seldom more than an hour or two.
In the process, a female mayfly will deposit an average of 4,000 fertilized eggs into Lake Erie. These eggs sink to the lake’s bottom where they rather quickly morph into nymphs. These nymphs themselves go through a series of molts before their genetic coding kicks in and they eventually rise to the lake’s surface to become adults whose sole function is to procreate, lacking any bodily equipment to feed.
Adult mayflies found in the Western Basin of Lake Erie come ashore – usually around evening - to find a hard surface onto which they can undergo their final molt. These mayflies then form immense swarms again offshore as they mate, said Justin Chaffin, the research coordinator for The Ohio State University’s Stone Laboratory at Put-in-Bay.
“Females typical die a couple hours after mating,” Chaffin said.
Indeed, mayflies are credited (or cursed) with the shortest lifespan of any of the Earth’s living creatures. So much so that science has designated the mayfly into the so-called order “ephemeroptera,” a word taken from Greek meaning “things that live for a day.”
Interestingly enough this ever-so-brief life as an adult has been recorded by the ancient Greek philosopher Aristotle and the Roman Empire historian Pliny the Elder. And Nineteenth Century clergyman and poet George Crabbe in his poem “The Newspaper” used the mayfly as an illustration for the ever-so briefly inspired content of the daily newspaper.
As for what people call them, the species has more than few localized and regional monikers. One that’s not so commonly used today as it was a number of decades ago is “Canadian soldier,” a reference to the fact that clouds of the insects lift from the waters of Lake Erie and move south over land. Other provincial names associated with the mayfly are “June bug,” “shadflies,” “one-day flies,” “burrowing mayflies,” and “fish flies.”
The mayfly is a well distributed freshwater-only creature, too. Science says the world has about 3,000 mayfly species of which around 700 exist in North America. They are comprised of 42 families in some 400 genera. Distant relations include dragonflies.
Chaffin says Lake Erie has two mayfly species, the first being a critter with the unwieldy scientific name of Hexagenia limbata and the other being the tongue-twisting Hexagenia rigida.
“The first one makes up about 90 percent or so of the mayflies you see in the Western Basin and the second about 10 percent, but to the untrained eye you really would not be able to tell the difference,” Chaffin said.
Why Lake Erie’s Western Basin has such an enormous population of mayflies while the Central Basin has far fewer, Chaffin said the former basin has considerably more of the shallow water habitat the insect prefers while the latter only has suitable habitat of less than one mile from shore.
Also, says Chaffin, mayflies demand well-oxygenated water which “is why you don’t find them in the Central Basin’s ‘Dead Zone.’”
And while an individual mayfly life is a candle that burns quickly from both ends, evolutionary scientists say the species as a whole extends back before the age of dinosaurs: more than 350 million years ago to the Carboniferous Period, or the age of amphibians. As such the mayfly is one of the oldest species of flying insects.
Mayflies also made it through the K/T Extinction of 65 million years ago, the event that evolutionary scientists say wiped out 75 percent of all the world’s lifeforms.
However, the Lake Erie mayfly of the mid-Twentieth Century had a tough go of it as well. Environmentalists, conservationists and sportsmen became alarmed in the 1950s and 1960s when the mayfly largely disappeared from Lake Erie, the victim of water pollution and the lack of dissolved oxygen. It wasn’t until the 1990s that the mayfly population rebounded.
“In western Lake Erie, mayfly populations dropped to essentially zero between 1959 and 1961, and remained extremely low until 1993, when scientists found about twelve mayfly larvae per square meter of sediment. Most recently, those numbers have increased dramatically, to 300-400 mayflies per square meter, a testament to environmental protection efforts and improving water quality,” says a March 8, 2018 story by the Ohio Sea Grant agency.
That mayflies contribute to the well-being of the environment where they exist there is no doubt.
“Mayflies are a vital link in the food chain of freshwater ecosystem, making energy stored in algae and other aquatic plants available to higher consumers,” says a Purdue University piece on the subject.
Chaffin added that as nymphs, mayflies take in muck, filtering out any organic matter. In the process they become the low-hanging fruit for virtually all sorts of aquatic predators. Among them are yellow perch.
And as the nymphs begin their ascent to the water’s surface to make their first molt into adulthood (called the subimago stage) they are feasted upon by more fishes, among them being the walleye.
Even as emerged adults molting for the last time on land, mayflies become the target of spiders, birds and the like, Chaffin said.
“Everything that swims in Lake Erie eats mayflies,” Chaffin said.
- Jeffrey L. Frischkorn
JFrischk@Ameritech.net
JFrischk4@gmail.com
